1,1-Dibromoethane → 8-(2-Bromoethoxy)-3,4-dihydro-2H-1-benzothiopyran

Tetrabutylammonium bromide (1.94 g 6 mmol; 0.2 eq.), phase-transfer agent, is added to a heterogeneous mixture composed of 8-hydroxy-3,4-dihydro-2H-1-benzothiopyran (5 g; 30 mmol), acetonitrile (30 ml) and a 1.6N sodium hydroxide solution (28.3 ml; 45 mmol; 1.5 eq.). Dibromoethane (10 ml; 60 mmol; 1.5 eq.) is added after 30 minutes' stirring, the stirring being continued for 24 hours at 30° C. Concentration of the various phases under reduced pressure at 25° C. is followed by extraction of the products with dichloromethane. Washing with a 5% sodium hydroxide solution allows a first purification, which is followed by purification over a silica column eluted with a 3:7 AcOEt/PE mixture, yielding the brominated title compound.